1. Field of the Invention
The present invention relates to a method and apparatus for alarming decrease in tire air-pressure. More particularly, it relates to a method and apparatus for alarming decrease in tire air-pressure capable of judging a decrease in air-pressure of a tire also when running on a bad road for ensuring safe driving.
2. Description of Background Art
When running on a bad road such as a snowy road or a gravel road, wheel speeds are disturbed through slip so that there might be made erroneous judgements that an air-pressure of a tire has decreased while the tire is actually of normal internal pressure. For preventing such instances, a conventional system for alarming decrease in tire air-pressure for detecting decompression of a tire (DWS) based on rotational information of four wheels introduces a logic for rejecting data obtained while running on a bad road (bad road reject). When running on a bad road, variations in wheel speeds are caused through factors such as slip, and such bad road reject serves to reject data upon determining that the vehicle is running on a bad road in case a rate of such variations exceeds a certain value.
The bad road reject might be such that, in case rotational speeds of a front left tire, a front right tire, a rear left tire and a rear right tire are respectively defined as V1(FL), V2(FR), V3(RL), V4(RR), calculations are performed every second for obtaining
(Front and rear wheel ratio on left)=V1(FL)/V3(RL)
(Front and rear wheel ratio on right)=V2(FR)/V4(RR)
xe2x80x83(Difference in front and rear wheel ratio between right and left)=(front and rear wheel ratio on left)xe2x88x92(front and rear wheel ratio on right)
Judged value of bad road=|(difference in front and rear wheel ratio between right and left)xe2x88x92(previous difference in front and rear wheel ratio between right and left)|,
wherein
(i) In case the judged value of bad roadxe2x89xa6threshold of good road
(1) A counter for normal good road surface (road surface that is not bad) is increment by 1.
(2) In case the counter for normal good road surface has reached 5, it is determined that it is a normal good road surface.
(3) Since values are maxing out, the counter for normal good road surface is set to 4, and counting is performed starting at step (1).
(ii) In case the threshold of good road less than judged value of bad roadxe2x89xa6threshold of bad road
(1) The counter for normal good road surface is set to zero.
(2) The previous judgement is maintained for judging whether the road surface is bad or good.
(iii) In case the threshold of good road less than judged value of bad road
(1) The counter for normal good road surface is set to zero.
(2) It is determined that the road surface is bad, and running data are rejected.
Other conditions for rejection are, for instance, low speed running, cornering, lateral directional acceleration (lateral G), acceleration or braking. Only running data which did not fall under these conditions for rejections are employed for judging air-pressure. An equation for obtaining a judged value which is used in judging air-pressure is given by
DEL={(V1(FL)+V4(RR))/2xe2x88x92(V2(FR)+V3(RL)/2)}/{V1(FL)+V2(FR)+V3(RL)+V4(RR)/4}xc3x97100(%)
In this manner, data were conventionally rejected when running on a bad road and judgements of air-pressure were not performed.
When running on a snowy road or a gravel load over a long period of time, no correct judgement of air-pressure can be performed owing to disturbances caused in wheel speeds so that no alarm can be issued even if a decrease in air-pressure has progressed to a remarkable extent, and it might happen that a driver is not aware of a blowout of tire until the tire finally bursts.
The present invention has been made in view of these facts, and it is an object thereof to provide a method and apparatus for alarming decrease in tire air-pressure capable of judging a decrease in air-pressure of a tire also when running on a bad road for ensuring safe driving.
In accordance with the present invention, there is provided a method for alarming decrease in tire air-pressure in which a decrease in internal pressure of a tire is detected on the basis of rotational information obtainable from wheels mounted to a vehicle and a driver is accordingly alarmed, wherein a plurality of thresholds for judging bad road are set.
In accordance with the present invention, there is further provided a method for alarming decrease in tire air-pressure in which a decrease in internal pressure of a tire is detected on the basis of rotational information obtainable from wheels mounted to a vehicle and a driver is accordingly alarmed, comprising the steps of: detecting rotational signals of respective tires, storing rotational information upon calculation of the rotational signals of the respective tires, setting a plurality of thresholds for judging air-pressure and setting a plurality of thresholds for judging bad road to meet the plurality of thresholds for judging air-pressure, judging, on the basis of rotational information of the respective tires, that the vehicle is running on a bad road, and judging decrease in air-pressure of a tire on the basis of a judged value which is calculated from the rotational information of the respective tires.
In accordance with the present invention, there is also provided an apparatus for alarming decrease in tire air-pressure in which a decrease in internal pressure of a tire is detected on the basis of rotational information obtainable from wheels mounted to a vehicle and a driver is accordingly alarmed, the apparatus comprising a threshold setting means for setting a plurality of thresholds for judging bad road.
In accordance with the present invention, there is yet further provided an apparatus for alarming decrease in tire air-pressure in which a decrease in internal pressure of a tire is detected on the basis of rotational information obtainable from wheels mounted to a vehicle and a driver is accordingly alarmed, comprising: a speed detecting means for detecting rotational signals of respective tires, an information storing means for storing rotational information upon calculation of the rotational signals of the respective tires, a threshold setting means for setting a plurality of thresholds for judging air-pressure and for setting a plurality of thresholds for judging bad road to meet the plurality of thresholds for judging air-pressure, a bad road judging means for judging, on the basis of rotational information of the respective tires, that the vehicle is running on a bad road, and a decompression judging means for judging decrease in air-pressure of a tire on the basis of a judged value which is calculated from the rotational information of the respective tires.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.